The invention relates generally to the field of recombinant viruses and induction of specific immunity, specifically to induction of tumor-specific immunity.
Tumor-specific cytotoxic T lymphocytes (CTLs) can prevent or eradicate tumors in a number of experimental systems and in patients with cancer (1-3). Clinical trials have demonstrated that 35% of patients with melanoma treated with specific, tumor-reactive lymphocytes can achieve either partial or complete tumor regression (4). The antigens recognized by the T cells have, in some cases, been identified (5, 6). Although cancer cells may express tumor-associated antigens (TAAs), CTLs directed against TAAs are not efficiently elicited by the growing tumor and, therefore, the immune system fails to control tumor growth. Thus, it appears that tumor cells lack either immunogenicity and/or the appropriate co-stimulation required for CTL activation.
In contrast to tumor cells, viruses are strong inducers of cellular immune responses. Thus, activation of the tumor-directed CTL response by vaccination with recombinant viruses expressing tumor-associated antigens is a promising approach for the prevention and treatment of malignancies. Viral vaccine vectors that have been successfully used in experimental cancer models include poxviruses, adenoviruses, picornaviruses and influenza viruses (7-10). However, because each vaccine vector may present its own set of beneficial and adverse properties, the search for new vectors continues to be an active area of research. For example, clinical use of some vectors currently under study may be limited by their record of safety, efficacy, potential oncogenicity or induction of immunosuppression. In addition, preexisting immunity against the vector could hinder the potency of treatment (8, 11), and therefore alternative viral vectors are needed.
There is a need in the field for viral vectors that can be used to induce immunity to a wide variety of antigens, including those present on tumors. The present invention addresses this need, and provides related advantages as well.
The present invention provides recombinant yellow fever viruses (YFV), particularly live attenuated recombinant YFV, which comprise exogenous (i.e., non-YFV) nucleotide sequences which encode exogenous (i.e., non-YFV) amino acid sequences. These recombinant YFV viruses comprise an exogenous nucleic acid. Infection of a host cell with a recombinant YFV provides for expression of the exogenous nucleic acid in a host cell and production of an antigenic polypeptide encoded by the exogenous nucleic acid. Such recombinant YFV are useful in eliciting an immune response to the exogenous polypeptide.
The recombinant live attenuated YFV express an exogenous nucleotide sequence which encodes an exogenous polypeptide, such as, but not limited to, a polypeptide obtained from a pathogenic agent other than YFV, a tumor antigen, and the like. These recombinant YFV are useful, when introduced into a mammalian subject, in eliciting an immune response to the exogenous polypeptide in the subject. Thus, the recombinant YFV of the invention serve as immunization vehicles.
A wide variety of antigenic amino acid sequences can be incorporated into the YFV polyprotein, including those of microbial pathogens (e.g., bacteria, parasites, viruses (other than YFV), fungi, and the like) and tumor-associated antigens. In general, following infection of a host cell by the recombinant virus of the invention, the exogenous polypeptide is proteolytically cleaved from the viral polyprotein precursor into which it is incorporated. The exogenous polypeptide may then be exported to the host cell surface, may be presented on the cell surface as a peptide with a major histocompatibility antigen, may be secreted from the cell, or may remain in the cytoplasm of the cell. In the context of tumor immunotherapy, expression of a exogenous polypeptide in a host elicits an immune response to the tumor, with the result that the tumor cell mass and/or tumor cell number is reduced, development of a tumor is prevented or delayed, and/or the probability that a tumor will develop is reduced.
The invention provides pharmaceutical compositions comprising recombinant YFV of the invention. Such compositions can be used, for example, to reduce the severity of disease, reduce the risk of clinical disease, prevent the onset of a disease and/or to ameliorate the disease via recruitment of the host immune system.
The invention also provides methods of eliciting an immune response to an antigen in a mammalian subject. Such methods comprise administering a recombinant YFV of the invention to a mammalian subject so as to elicit an immune response to the exogenous polypeptide. The antigen can be a host antigen or an antigen of a non-YFV pathogen.
The invention further provides methods of reducing or inhibiting tumor cell growth, and methods of reducing tumor cell mass and/or tumor cell numbers. Such methods comprise administering a recombinant YFV of the invention which comprises exogenous sequences encoding a tumor-associated antigen (TAA)/epitope to a host bearing a tumor, such that the recombinant YFV enters a cell of the host and the exogenous TAA polypeptide is expressed on the surface of a host cell, is presented in the context of an MHC molecule, or, alternatively, secreted from the host cell. An immune response is elicited to a tumor which bears on its surface an antigen which comprises the exogenous TAA polypeptide or which resembles the exogenous polypeptide sufficiently to elicit an immune response toward the tumor cell. The immune response to the tumor bearing the tumor-associated antigen on its surface is sufficient to reduce, inhibit, or eliminate the tumor.
The invention further provides methods of preventing tumor cell growth, and methods of reducing the probability that a tumor will form, comprising administering a recombinant YFV of the invention, which comprises a tumor-associated antigen/epitope-encoding nucleic acid, to a host not bearing a tumor, such that the recombinant YFV enters a host cell, the tumor-associated antigen is expressed on the host cell surface and/or presented in the context of an MHC molecule (e.g., MHC Class 1), and an immune response is elicited to the tumor-associated antigen. The immune response to the tumor-associated antigen is sufficient to prevent, or reduce the likelihood, of tumor development in the host.
A primary object of the invention is to provide a recombinant YFV that provides for production of an exogenous polypeptide that is suitable for induction of an immune response to the polypeptide in a host following infection with the recombinant YFV. Such exogenous polypeptides include, but are not limited to, an antigen produced by the host (e.g., a tumor antigen), or an antigen from a non-YFV pathogen (e.g., a retroviral antigen).
An advantage of the invention is that the recombinant YFV of the invention are live attenuated virus, which will continue to propagate until the intervention of the host""s immune system.
Another advantage of the invention is that the YFV exhibits low toxicity in vivo.
Yet another advantage of the invention is that the YFV can express a polypeptide inside the host cell, and thus can provide for induction of an immune response, particularly a cellular immune response that involves, for example, antigen-specific cytotoxic T lymphocytes (CTLs).
Yet another advantage of the invention is that the immune response elicited using the YFV of the invention is not limited to the infected cells, as the immune system will also recognize cells ea ring the antigen expressed by the recombinant YFV. For example, the production of a tumor antigen by the recombinant YFV can xe2x80x9cbreak immune tolerancexe2x80x9d to tumor antigens, and induce an immune response against the tumor effective to, for example, inhibit tumor growth.
These and other objects, advantages, and features of the invention will become apparent to those persons skilled in the art upon reading the details of the invention as more fully described below.